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Discussion Starter · #1 ·
I crashed the bike (Giant TCR) last thursday. The frame is gone, cracks in the seat tube.
Currently I ride an M, but when I had a fitting recently, the fitter said that the (horizontal) top tube length was on the limit for my flexibilty. Although the current length works, a bit shorter would be better (almost certainly less flexible in the future).

Now, an M has:
seat tube angle: 73°
horizontal top tube: 555 mm
reach: 386 mm
stack: 552 mm
stem: 100 mm

A shorter stem doesn't work, it makes the bike unbalanced. Position of the saddle is relatively far forward.

An S has:
seat tube angle: 73,5°
horizontal top tube: 535 mm
reach: 377 mm
stack: 534 mm
stem: ???

The difference in top tube length is 20 mm, but the difference in reach only 9 mm. Assume I buy an S. Would an 110 mm stem work, in combination with a saddle that is moved backwards?
I have some toe overlap now. Nothing that worries me when I'm riding, but would it get much worse?
 

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Don't worry about toe overlap. You only need to be aware of it while doing trackstands at stoplights or U-turns in tight quarters. You'll NEVER clip the front wheel while riding.

As far as the stem goes; use the existing stem. It won't cost you anything, and it sounds like you're at the limit of your reach as your bike is currently set up.

Warning: Don't fall into the trap of slamming your stem. Wide differentials in saddle to bar drop require a shorter stem. With the smaller frame you'll want more spacers under the stem to at least equal the drop of your current bike.
 

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You need to consider head tube height also. In other words and more specifically "stack". If they geo chart has those number focus on them.

Also consider seat tube angle. But it sounds like you already know that because you recognize the difference in top tube length is not the same as the difference in reach.
 

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Discussion Starter · #4 ·
You need to consider head tube height also. In other words and more specifically "stack". If they geo chart has those number focus on them.

Also consider seat tube angle. But it sounds like you already know that because you recognize the difference in top tube length is not the same as the difference in reach.
Indeed, the difference in stack between S and M is 18 mm. That's a lot of spacers.
I don't think seat tube angle is important. I used my old pocket calculator and moving the saddle 6 mm or so would correct for the difference between 73° (M) and 73,5° (S).
 

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I'm 5'8" and ride 50cm road and cross bikes.
I don't mind a lot of drop, but I like really short reaches. So I ride my bike with a 90cm stem with a plus 6 degree rise, or more.
When looking at a new bike, I compare the effective top tube length. Then i get a stem to match. While not sexy, you can always grab one of those adjustable stems, and ride a few times with it and change it around to see what reach and drop is best.
Or, frankly, keep trying different stems as your can find perfectly light and functional Al ones for $20.

My current road bike has toe overlap. I track stand multiple times per ride, so it's annoying. I've learned to do it with my front toe pointed down, but it's annoying. Not all 50cm bikes have this issue. If you get the geometry of the frame, your can measure how far past your toes go from the pedal axle and figure out if you'll have overlap on a specific bike.

Last thing I'll say is that carbon cash be repaired, and depending on paint etc, it can be done so it's just as strong or stronger, and unnoticeable. My personal preference is carbonframerepair.com.
 

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Also, I forgot to add that in general the saddle position is totally based on your legs - change reach and drop using the steer tube spacers, stem, and bars.
 

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Also, I forgot to add that in general the saddle position is totally based on your legs - change reach and drop using the steer tube spacers, stem, and bars.

This!!! Never adjust your saddle in order to get closer to the handlebars!

Reach and Stack are by far your most important geometry specs to pay attention to. My question here would be does the M fit in other respects - can you get to the correct distance between your saddle and pedals? Is your fore/aft saddle position correct? How much seat post is showing?
 

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Discussion Starter · #8 ·
This!!! Never adjust your saddle in order to get closer to the handlebars!

Reach and Stack are by far your most important geometry specs to pay attention to. My question here would be does the M fit in other respects?
The position of the saddle on the M is relatively far forward, but since my fitting it's correct for my weird legs. I'm not planning to change it.
I understand that the position of the saddle relative to the bottom bracket (measured horizontally and vertically) should stay the same, regardless of the top tube length. So it's only the reach that matters in that respect.
But it's remarkable that a difference of 20 mm in top tube length leads to a relevant difference of only 9 mm (the difference between the reaches of the S and the M).

Last thing I'll say is that carbon cash be repaired, and depending on paint etc, it can be done so it's just as strong or stronger, and unnoticeable.
My bike is in the bike shop, so I haven't seen it yet. They only called me to tell that there are cracks in the seat tube. I called a few carbon repair people. They made clear that a seat tube is problematic. Repairs are done on the inside, meaning that there's always the possibility that the saddle stem won't fit after the repair.
 

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The position of the saddle on the M is relatively far forward, but since my fitting it's correct for my weird legs. I'm not planning to change it.
I understand that the position of the saddle relative to the bottom bracket (measured horizontally and vertically) should stay the same, regardless of the top tube length. So it's only the reach that matters in that respect.
But it's remarkable that a difference of 20 mm in top tube length leads to a relevant difference of only 9 mm (the difference between the reaches of the S and the M).



My bike is in the bike shop, so I haven't seen it yet. They only called me to tell that there are cracks in the seat tube. I called a few carbon repair people. They made clear that a seat tube is problematic. Repairs are done on the inside, meaning that there's always the possibility that the saddle stem won't fit after the repair.
I'd figure they could figure out a way to dremel down in there, but maybe it's too much of a pain.
 

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The position of the saddle on the M is relatively far forward, but since my fitting it's correct for my weird legs.
If this is true, you must have very short femurs relative to the rest of you. All of my bikes have the saddle just about as far back as it can go in order to fit me.
 

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If this is true, you must have very short femurs relative to the rest of you. All of my bikes have the saddle just about as far back as it can go in order to fit me.
It depends on the position you like as well. KNOP is a starting place, but moving the saddle forward and up maintains the same distance between saddle and BB. A more forward and higher position is more of the time trial/ triathlon style.
 

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It depends on the position you like as well. KNOP is a starting place......
You do mean KOPS (Knee Over Pedal Spindle), correct?

....but moving the saddle forward and up maintains the same distance between saddle and BB. A more forward and higher position is more of the time trial/ triathlon style.
If this is true, that would explain things since I'm more of an long endurance rider who likes doing plenty of hills. I rarely, if ever pedal out of the saddle.
 

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Discussion Starter · #14 ·
I don't know why exactly the saddle is so far forward, but my fitting wasn't based on formulas like KOPS. They took a more holistic approached, looking at the center of gravity of my body etc. On of the strange results is that my bike handles better now.
 

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I don't know why exactly the saddle is so far forward, but my fitting wasn't based on formulas like KOPS. They took a more holistic approached, looking at the center of gravity of my body etc. On of the strange results is that my bike handles better now.
If it fits, it fits. Everybody's different.
 

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You need to consider head tube height also. In other words and more specifically "stack". If they geo chart has those number focus on them.
This is why I went up a size with my current bike. You mentioned less flexible. I needed a taller head tube to accommodate my lack of flexibility, and simply used a shorter stem. The bike fits and rides great! You'll get warnings that going with a shorter stem will compromise handling, but I can't agree with that based on experience. If you go down in size, you might need a stem with more rise to help offset the shorter stack.
 

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Oh, another easier suggestion is to go with the Defy over the TCR if you go down in size. That'll make the stack much easier to handle.
 

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I don't know why exactly the saddle is so far forward, but my fitting wasn't based on formulas like KOPS. They took a more holistic approached, looking at the center of gravity of my body etc. On of the strange results is that my bike handles better now.
Indeed, for shizzle. I think it's a Bontrager idea to consider CG, rather than just where your knee is. If I recall, he also noted that stem length relates to your out-of-the-saddle position as well. I've noticed on different bikes that I can adjust to slight differences in reach fairly easily when seated, but that same slight difference feels downright wonky when standing.
 

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You'll get warnings that going with a shorter stem will compromise handling........

I've heard this warning over and over again. I've never found it to be true.

Oh, another easier suggestion is to go with the Defy over the TCR if you go down in size. That'll make the stack much easier to handle.
Well yes, the Defy is an endurance bike, the TCR is more of a race bike. So if you look at the geometry on the same size on both bikes, you will see the Defy has a greater stack and shorter reach than the TCR.
 
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